Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous translumenal angioplasty (PTA) and percutaneous translumenal coronary angioplasty (PTCA). These therapeutic techniques are well-known in the art and typically involve the use of a balloon catheter with a guide wire, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached to its distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
Vascular restrictions that have been dilated do not always remain open. For example, the restriction may redevelop over a period of time, a phenomenon commonly referred to as restenosis. Various theories have been developed to explain the cause for restenosis. It is commonly believed that restenosis is caused, at least in part, by cellular proliferation over a period of time to such a degree that a stenosis is reformed in the location of the previously dilated restriction.
Intravascular radiation, including thermal, light and radioactive radiation, has been proposed as a means to prevent or reduce the effects of restenosis. For example, U.S. Pat. No. 4,799,479 to Spears suggests that heating a dilated restriction may prevent gradual restenosis at the dilation site. In addition, U.S. Pat. No. 5,417,653 to Sahota et al. suggests that delivering relatively low energy light, following dilatation of a stenosis, may inhibit restenosis. Furthermore, U.S. Pat. No. 5,199,939 to Dake et al. suggests that intravascular delivery of radioactive radiation may be used to prevent restenosis. While most clinical studies suggest that thermal radiation and light radiation are not significantly effective in reducing restenosis, some clinical studies have indicated that intravascular delivery of radioactive radiation is a promising solution to the restenosis enigma.
Since radioactive radiation prevents restenosis but will not dilate a stenosis, radiation is preferably administered during or after dilatation. European Patent No. 0 688 580 to Verin discloses a device and method for simultaneously dilating a stenosis and delivering radioactive radiation. In particular, Verin '580 discloses balloon dilatation catheter having an open-ended lumen extending therethrough for the delivery of a radioactive guide wire.
One problem associated with the open-ended lumen design is that bodily fluids (e.g., blood) may come into contact with the radioactive guide wire. This may result in contamination of the bodily fluid and require the resterilization or disposal of the radioactive guide wire. To address these issues, U.S. Pat. No. 5,503,613 to Weinberger et al. proposes the use of a separate closed-ended lumen in a balloon catheter. The closed-ended lumen may be used to deliver a radioactive guide wire without the risk of contaminating the blood and without the need to resterilize or dispose of the radiation source.
The closed-ended lumen design also has draw backs. For example, the addition of a separate delivery lumen tends to increase the overall profile of the catheter. An increase in profile is not desirable because it may reduce flow rate of fluid injections into the guide catheter and it may interfere with navigation in small vessels.
Another problem with both the open-ended and closed-ended devices is that radiation must travel through the fluid filled balloon in order to reach the treatment site. While this is not a problem for gamma radiation, it poses a significant problem for beta radiation which does not penetrate as well as gamma radiation. Beta radiation is considered a good candidate for radiation treatment because it is easy to shield and control exposure. In larger vessels (e.g., 0.5 cm or larger), a fluid filled balloon absorbs a significant amount of beta radiation and severely limits exposure to the treatment site.